Bi-metal control



Aug.- Z, 1957 w. A. RAY 2,803,495*

BI-METAL CONTROL.

Filed Jan. 11, 1955 INVENToR.

MLM/w A. Bmg

' TTOQNEYS.

United States Patent 4vC) isi-METAL coNrRoL William A. Ray, North Hollywood, Calif., assignor to General Controls Co., a corporation of California Application January 11, 1955, Serial No. 481,104

1 Claim. (Cl. 297-12) This invention relates to a thermally responsive mechanical operator cooperable with a liquid container, such as a tank, for opening and closing lfuel valves or the like.

-In operators of this character, it has lbeen common to provide two members, a tube projecting into the boiler and a rod in the tube having its inner end :aixed to the inner end of the tube, and its -outer end connected to the valve closure. The material of the tube has a coeiicient of expansion diierent from that of the rod. The differential expansion or contraction provides small movement necessary to operate the valve or other device for controlling the intensity of heating, in accordance with the temperature of the medium.

Expensive materials having very low coeticient of thermal expansion are commonly used. But even with such special materials, long tubes and rods are still required in order to realize sucient movement of the mechanism.

It is an object of this invention to provide a thermal control mechanism which -achieves a materially greater thermal movement of the mechanism per unit length thereof than has been achieved by prior devices. This is made possible by an arrangement in which one composite member of the mechanism is foreshortened by thermal expansion of its parts, 'and the other member in the usual manner elongates upon thermal expansion. Furthermore, the composite member itself achieves a range of movement very much greater than that due to simple thermal expansion. This is achieved by an arrangement of parts to be hereinafter described. In this organization the thermal changes in lengths of the elements are additive, achieving substantial movement of the device.

It is another object of this invention to provide a simple inexpensive device of this character in which the use of expensive materials is minimized.

fIt is another object of this invention to make it possible to provide a thermal control mechanism that is more compact than heretofore Ihas been possible, all without sacrice of operating characteristics.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of one embodiment of the invention. For this purpose, there is shown a lform in the drawings `accompanying and forming part of the present specification. This form will now be described in detail, illustrating the general principles of the invention; 'but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of this invention is bes-t deiined by the appended claim.

A.Referring to lthe drawings:

Figure l is a longitudinal sectional view of a thermal control unit embodying the present invention, shown in cooperation with a water heater tank and a fuel valve;

Fig. 2 is a fragmentary sectional view of the unit, showing an alternate position; and

Fig. 3 is a transverse sectional view, taken along the plane indicated by line 3 3 of Fig. 1.

In Fig. 1 there is shown a fragment of a water heater ICC tank containing a body of water 11. The usual shell and the insulation between the tank and shell are not shown.

A tubular member 12 projects into the tank 10, having a substantial portion of its exterior surface exposed to the water 11 in the tank. The left-hand outer end of the tubular member 12, `as viewed in Fig. 2, is exteriorly threaded for cooperation with a thickened portion 13 of the wall of the tank 10.

A plug 14 closes the otherwise open right-hand inner end of the tubular member 12 and supports a pair of elongate flexible bimetal strips 15 and 16 in the tubular member 12. For this purpose, corresponding ends 17 and 18 of the lbimetal strips are together received in a rectangular recess or slot 19 formed in the inner survface of the plug 14. The lbimetal strips 15 and 16 extend longitudinally of the tubular member 12 and have Itheir other corresponding ends 20 and 21 held together and received in a rectangular recess or slot 22 of a movable support 23.

The movable support 23 on the opposite side of the bimetal strips 15 and 16 has a circular recess 24 mounting a rod 25 for operating a valve mechanism. The rod 25 is guidingly accommodated in a through 4aperture 26 of an inwardly directed ange 27 formed adjacent the lefthand outer end of the tubular member 12.

The ibimetal strips 15 and 16 are symmetrically disposed about a plane extending through the axis of the tubular member 12, the fiat surfaces of the strips opposing each other. The outer elements 15a and 16a of the lbimetal strips 15 and 16 are respectively of a material having `a higher coeicient of thermal expansion than the inner elements 15b and 1Gb. The elements of each bimeta'l strip 15 and 16 are welded or otherwise firmly secured together.

For a certain relatively low temperature, the bimetal elements of each strip 15 and 16 are iiat. Upon a rise in temperature, the strips assume an arcuate or bowed configuration due to dierent stresses in the elements of the strips caused by their interconnection and different coeiicients of thermal expansion. The extent of bowing is dependent upon the flexibility of the strips, which is sufficiently large to permit substantial bowing. The strips 15 and 16 bow in opposite outward directions, those elements 15a and 16a having the higher coefficient of thermal expansion being outermost.

The outer ends 20 and 21 of the strips normally tend to move arcuately, but are prevented from doing so since they are held together by the support 23; and, since the strips 15 and 16 are symmetrically disposed, the forces exerted by the strips in a direction normal to the plane of symmetry counterbalance each other.

The difference in the coeicients of expansion between the elements of each strip is sufficiently large with respect to other physical constants of the elements, to cause the ends 20 and 21 to move toward and away from the fixed ends 17 and 18 in accordance respectively with a rise or fall in temperature. The stress dierences are suciently great to produce columnar type strain, in an axial direction, more than counterbalancing elongation due to thermal expansion. Furthermore, by appropriately designing the strips, the per unit columnar type shortening and corresponding elongation may be many times greater than that due to simple rectilinear thermal expansion and contraction of a bar. The strips together thus may provide a very substantial per unit movement.

Accordingly, upon an increase in temperature, the strips 15 and 16 bow to a greater extent and move the ends 2.0 and 21 of the strips toward the inner end of the tubular member 12. Also, the tubular member 12 expands upon an increase in temperature, carrying the plug 14 and the bimetal strips 15 and 16 toward the right, as

viewed in Fig. l. These eiects add together to move'the I Operating rod 2S toward the inner end of the tubular member. The contribution due to the bowing of the strips V15 and 16 maybe many ,timesk greater than thatvdue to 'thet'bla'r' member 12. Similarly, uponadecreaseiin temperature, Vthe thermal effects of the strips 1`S`and16 and-the tubular member 12 add together to move the rod 25 in the other'direction.

The strips 15and 16 are bowed more or lessY throughout the voperating temperature range of the apparatus.

ln'Fig; l the thermal control unit is subjected to a high temperature, causing the bimetal strips 15 and 16 to bow outwardly. The rd`25 is moved inwardly.

i In the position shown in Fig. 2, the unit is subjected to alower temperature, causing the bimetal `strips and 1'6 to be bowed only Vto a small extent. The rod 25 is rr'xoved'outwardly.Y

Theleft-'hand end of the support '23 has sucient clearance with respect to the inwardly directed flange 27 of the tubular member 12 as to permit appropriate axial movement of the rod 2'5. The diameter of the tubular member 12 -is suliciently large to permit substantial bowing of the strips. `The interior of tube'12 is vented, as indicated vby vent 50.

-The movement of the-rod 25 is availed of to operate a valvestructure located'within a hollow split valve casing 278. The valve casing 28 has a valve chamber opening outwardly of thebody at 29. The anged end of the tubular member 12 tits in correspondingly shaped grooves 30 at the valve body opening V29. VThe tubular member is assembled with the casing 28 by closing the split casing about the anged end of the tubular member. The end of the tubular member 12 effectively closes and denes therchamber formed in the valve body'S.

An O-ring 31, carried between peripheral spaced anges 32 of the tubular member 12, cooperates with a cylindrical surface of the body opening 29 to ensure a sealing relationship. Suitable sealing means 33 prevents undesired passage of fluid between the rod 25 and the aperture 26 of the inwardly directed flange 27.

The rod 25 cooperates at its outer end with an actuator 34 which, in turn, cooperates with a snap disc 35 engageable with the stem 36 carrying a closure structure 37. A compression spring 38, the tension of which may be adjusted, urges the closure 37 toward seating position with respect to a seat-forming member 39 and, through the V2,803,495 'Y n v ,4 I stem 36, moves the disc to the position shown in Fig. 1 upon withdrawal of the rod 25. The valve vstructure shown in the present instance is by way of example only, as numerous other forms of snap action valves can be operated to open and close by movement of rod 25 respectively toward the left and toward the right.

By the aid of the present apparatus, a substantial movement of the rod 25'is achieved per unit length of the tubular member 1.2. VThis is made possible by virtue of the additive relationship between the thermal properties of the tubular member itself and the bimetal strips 15 and 16. Conveniently, the thermal control unit may be sufficiently short to be compactly accommodated'inboiler structures havingonly limited spacesuch as due to ue tubes from the re box, to accommodate the thermal unit.

The inventor claims:

In apparatus of the character described: an elongate tubular member having exterior threads adjacentone end, the other end being openjthe tubularmember being imade of material having a high temperature coeicientV of expansion; a thermally conductive plug closing the openend of the member, and .exposed exterio'rly of the member, said plug having an inner surface provided with a slot; a pair of strips each comprising elements having different coefficients of thermal expansion, corresponding rst ends of the strips being fitted in the slot of said plug, the sti-,ips extending symmetrically and longitudinally Vtoward said one end of said member; the strips having surfaces opposing each other; those elements of the respectiveV strips having like coeiiicients of expansion being located correspondingly with respect to the plane of symmetry; and a load actuator at said one end of said member andhaving a surface provided with a slot, the corresponding other ends of the strips Ybeingr itted in the slot of said actuator for connecting the actuator to the strips, the actuator coniining the said corresponding other ends of the strips for movement together.

References Cited in theflle of this patent UNITED STATES PATENTS K 1,883,250 Spencer Q Oct. 18, 1932 2,216,809 Derby Oct. 8, 1940 2,486,714 Koei NOV. l, 1949 2,661,243 Fox Dec. l, 1953 

